Bosch Start-Stop Coasting System

A new Bosch start-stop system stops the engine when the vehicle is traveling at speed, helping to reduce fuel consumption by 10 percent.

Tests carried out by Bosch have shown that combustion engines runs needlessly about 30 percent of the time, meaning that the vehicle could simply coast for about a third of every journey.

Although these phases are not taken into account in the New European Driving Cycle (NEDC), under real traffic conditions the function will give drivers a roughly 10 percent fuel saving.

“The start-stop coasting function is affordable, can be combined with any type of combustion engine, and substantially reduces fuel consumption,” says Dr. Rolf Bulander, member of the board of management of Robert Bosch GmbH. He added, “Start-stop coasting will become an everyday feature in cars – just like air conditioning.”

Zero-emission, noise-free, low-resistance

With its new start-stop coasting function, Bosch enables drivers of vehicles with combustion engines to travel in zero-emission, noise-free, and low-resistance mode over large parts of their journey. The technology stops the engine when the vehicle is in motion, so that it does not consume any fuel. Whenever the vehicle can maintain its speed simply by rolling – for instance on a gentle incline – the engine is stopped. As soon as the driver touches the gas or brake pedal, the engine starts up again.

Much of what makes the system innovative is its enhanced software and the use this makes of existing sensor data. Furthermore, the start-stop starter has been configured to cope with greater loads and to deliver faster restarts.

In other respects, the system requires few additional components and can be integrated in just about any vehicle in the world. Whether they drive diesel-powered cars in Europe, gasoline models in North America, or CNG-powered vehicles in Asia, drivers everywhere stand to benefit from the new technology – as does the environment.

Reduced fuel consumption also means lower CO2 emissions. In Germany, some three million new vehicles were sold in 2012. According to statistics, the annual average distance driven is around 11,500 kilometers. If every new car were equipped with the coasting system and emitted just ten grams less CO2 per kilometer as a result, the theoretical annual reduction in CO2 would amount to over 30,000 metric tons.

Today, thanks to double-clutch transmissions, some vehicles already have a “light” version of the coasting system on board. As soon as the drivers take their foot off the gas pedal, the system switches the engine to idle. While this means the vehicle is doing no more than rolling, it is still consuming fuel in order to keep the engine ticking over.

Bosch start-stop systems stop the vehicle’s engine altogether. The first generation of the system stops the engine only when the vehicle is completely stationary, while the enhanced start-stop system cuts the engine as soon as the vehicle is coasting to a halt – for instance at a red light. In contrast, as soon as the driver’s foot is off both the gas and the brake pedal, vehicles equipped with the new start-stop coasting function stop the engine while the vehicle is in motion. That saves even more fuel. And because the engine is disengaged, the vehicle can coast for longer than it could with an overrun fuel cutoff system, for example.

Bosch is embedding fuel-saving functionality in many of its products. One example is eClutch, which makes it easy to offer the coasting function even in vehicles with manual transmissions. As soon as a coasting phase is possible, eClutch decouples automatically and the engine is stopped.

The coasting function is also available as an add-on for the Bosch entry-level hybrid, the boost recuperation system, to help it save even more fuel. Equipped with a more powerful generator and a compact lithium-ion battery, the 48-volt hybrid saves around 15 percent of fuel through electrification alone. In real traffic conditions, and fitted with the coasting function that shuts down the engine, the hybrid can achieve fuel savings of an additional ten percent – or 25 percent overall.